This invention relates to engine piston compression rings having modified gap end configurations.
It is known in the art relating to engine piston compression rings that joints between the ring ends should allow enough space to normally avoid ring gap end butting. The traditional approach used to minimize end butting has been to increase the gap size between the ring ends. However, increasing the gap size between the ring ends increases the amount of combustion gas blowby.
Various types of ring joints have been used including lap joints, angle joints, seal joints, and butt joints. However, modified ring joints may still allow end butting to occur under severe conditions such as low temperature cold starting and warm up.
The present invention provides engine piston compression rings which can minimize negative effects of ring gap end butting while optionally providing smaller ring gaps and reduced gas blowby in normal operation.
The invention controls deflection of the ring ends by using an angled joint and a relieved ring end. The angled joint and an appropriately placed relief area allow the relieved ring end to deflect a substantial distance after butting of the ring ends and before the relieved end engages a wall of an associated ring groove of the piston. The direction of deflection is controlled by the angle and direction of the ring joint. Deflecting the relieved portion of the ring end allows additional relative ring expansion after ring end butting without increasing the ring load against the cylinder bore. Thus, harmful effects of end butting are minimized and the gap between the ring ends can be reduced, resulting in reduced blowby.
In one embodiment of the invention, a compression ring has a gap that forms an angle with respect to a radius drawn from a longitudinal axis. Butting of the ring ends at the gap causes one end of the ring to be deflected inward and that one end is relieved for a portion along an inner edge. The relieved portion slopes outward toward the ring end where the radial thickness of the ring is smallest. This design creates end relief, which allows the relieved end of the ring to bend into the annular piston ring groove instead of increasing ring load against the cylinder bore.
A variation of the previously described embodiment has a slot adjacent the relieved portion that extends outward from the inner edge to promote bending of the relieved end. This slot decreases the force required during end butting to move the relieved end inward toward the piston instead of increasing ring load against the cylinder bore.
In another embodiment of the invention having a similarly angled gap, the relieved portion is generally circumferential with a transition portion to the full ring thickness. This design creates end relief, which allows the relieved end to bend a greater distance than the previous embodiments.
In a differing fourth embodiment, the compression ring has a gap that forms an angle with respect to the longitudinal axis of the ring. Butting of the ring ends at the gap causes one end of the ring to slide up on the angled other end so that the one end is relieved for a portion along the upper side of the ring. The relieved portion slopes downward toward the ring end where the longitudinal thickness of the ring is smallest. This design creates a form of end relief which allows the relieved end of the ring to slide toward the top of the annular piston ring groove instead of bending in toward the inner diameter of the ring groove like the other embodiments referred to.
The invention is particularly useful in avoiding negative effects of ring end butting which may occur under severe low temperature cold engine starting and warm-up conditions. However, it can also reduce effects of end butting under other conditions and may be used to reduce ring gap dimensions with resulting reductions of gas blowby during normal engine running.